incorporate a company by registering under the Register of companies. For details i refer you to go thru www.mca.gov.in where you would get details perrtaining to incorporation of company and filing certain forms with ROC. Consult a lawyer/CA firm as they deal with company matters.
It is your choice to firm , the Partnership Firm, or
Company, like Private Limitied Co., or Public Limited Co., if you want to pool the money from public , you have to opt for Public Limited Company, and it should be registered with the Company's registerar.
Partnership Firm registeration is with the Sales Tax Department of the concerned state.
Both the Partnership Firm, Sole Proprietor and Companies are covered to Indian Income Tax Act.